Kenaf (Hibiscus cannabinus L., Malvaceae) is a warm season annual
closely related to cotton (Gossypium hirsutum L.) and okra
(Abelmoschus esculentus L.). Initial interest in kenaf in the United
States was as a domestic supply of cordage fiber as a jute substitute in the
manufacture of rope, twine, carpet backing, and burlap (Wilson et al. 1965).
Later, kenaf was identified as a very promising fiber source for production of
paper pulp (Nieschlag et al. 1960; White et al. 1970). Researchers have
processed kenaf fibers into both newsprint and bond paper (Bagby et al. 1979;
Clark et al. 1971). Agricultural research starting in the early 1940s focused
on the development of harvesting machinery, high yielding anthracnose resistant
cultivars, and cultural practices for kenaf as a cordage crop (Nieschlag et al.
1960; White et al. 1970; Wilson et al. 1965).

In addition to the use of kenaf for paper pulp and cordage, researchers have
investigated its use as an animal feed (Killinger 1967; Phillips et al. 1989,
1990; Webber 1990b), a poultry litter (Tilmon et al. 1988), and as a bulking
agent for sewage sludge (Webber 1990a). Additional products that could
possible use kenaf as a raw material include automobile dashboards, carpet
padding, corrugated medium (Kugler 1988) and as a "substitute for fiberglass
and other synthetic fibers" (Scott and Taylor 1988).

The United States acceptance of kenaf as a commercial crop would be
strengthened if additional uses for kenaf can be established in the United
States. These and other possible kenaf uses need to be further investigated to
increase the potential use of kenaf plant products in the United States and
therefore encourage the commercial establishment of the kenaf industry.

Starting in 1988, the Ladonia Market Center, Ladonia, Texas, has conducted
kenaf research, development, and demonstration work. In addition to expanding
the list of possible uses of kenaf fibers, the Ladonia Market Center is a
primary proponent of kenaf as a livestock feed. Kenaf demonstration projects
have included kenaf production, harvesting, processing, and product
evaluations.

Fiber and Forage. In addition to cooperative research with the USDA
evaluating kenaf cultivars and their protein content, the Ladonia Market Center
was involved in a demonstration project evaluating the effect of row spacings
on kenaf dry matter yields. Production size (10 ha) kenaf plantings produced
10.3 t/ha on 25-cm row spacings and 14.0 t/ha on 76-cm row spacings when
harvested at 97 days after planting as a forage crop.

Seed. Ladonia Market Center has also demonstrated the feasibility of
producing seed from photo-insensitive kenaf cultivars in northern Texas.
Typically, photosensitive kenaf cultivars are preferred for use in the
production of kenaf fiber in the United States. Two of these cultivars,
'Everglades 41' and 'Everglades 71', were developed by USDA researchers (Wilson
et al. 1965) to extend the growing season of kenaf plant before the plants
initiate flowering. These photosensitive cultivars initiate flowering when
daylengths decrease to approximately 12.5 h, mid-September in southern states
(Scott 1982). In photosensitive cultivars, the initiation of flowering results
in plant growth reductions (Dryer 1967). Because of late floral initiation and
inability to produce mature seed prior to a killing frost, seed production in
the United States for these cultivars is limited to southern Florida, the Lower
Rio Grande Valley of Texas, and southernmost Arizona and California (Scott
1982).

Unlike photosensitive cultivars, photo-insensitve cultivars (i.e. Guatemala
series) can initiate flowering and produce mature seed before a killing frost
(Dempsey 1975). Photo-insensitive cultivars such as 'Guatemala 4', 'Guatemala
45', 'Guatemala 48', 'Guatemala 51', 'Cuba 2032' can initiate flowering after
100 days and prior to a decrease daylength of 12.5 h (Dryer 1967; Dempsey
1975). Photo-insensitive plants can, therefore, be planted during May or early
June and still have ample time to produce mature seed. The earlier production
of mature seed for photo-insensitive cultivars greatly expands the potential
seed production areas. After floral initiation, photo-insensitive cultivars
continue to grow without as much reduction in growth rate as with
photosensitive cultivars (Dryer 1967; Webber 1990b). As a livestock feed,
kenaf is often harvested at an earlier stage of growth than as a fiber crop, 60
to 90 days after planting (DAP) compared with 120 to 150 DAP (Webber 1990b). A
shorter growing season for kenaf as a livestock feed enables a producer to use
kenaf cultivars of the photo-insensitive group to produce equivalent dry matter
productions as with photosensitive cultivars while using seed that can be
produced further north and in a larger geographic area (Webber 1990b). Seed
production of photo-insensitive cultivars in more northern areas is often
overlooked as a result of the demand for and production of photosensitive
cultivar seed which cannot be typically produce outside a few selected southern
locations (Scott 1982).

The evaluation of field equipment for use with kenaf continues to be an
important aspect in commercializing kenaf. Standard cutting, chopping, and
baling equipment can be used for harvesting kenaf as a forage and fiber crop.
Kenaf was baled into both small square and large round bales. It is an
economic advantage to use presently available commercial harvesting equipment
if possible rather than investing in the development and production of kenaf
specific equipment. Appropriate harvesting equipment is readily available
throughout the United States, and the on-farm cost can be distributed over that
of other crops produced on the farm.

Research demonstrated the feasibility of pelletizing kenaf as a fiber and
forage crop. Pelletizing kenaf increases the density of the kenaf plant
material, reducing both transportation and storage costs. Kenaf stalks and
whole plants (stalks and leaves) were pelletized with standard commercial
equipment in widespread use for existing livestock feeds. Kenaf stalks with an
initial density of 0.31 g/cm3 were transformed into pellets with a
13.2 mm diameter and a density of 1.21 g/cm3, a 390% increase in
density. Whole plant kenaf, produced as a livestock feed, was pelletized into
pellets with a 10.4 mm diameter and a density of 1.22 g/cm3, a 395%
increase in density. The pelletizing research is an important element in
moving the harvested kenaf crop from the field to a packaged kenaf product.

In addition to processing and product development work with kenaf as a
livestock feed, Ladonia Market Center developed kenaf particle boards (K-Board)
of various densities, thicknesses, and fire and insect resistances. Kenaf
fibers were also successfully used in product development evaluations with
extraction molded plastics.

Cahilly (1967) reported that the amino acid composition of kenaf was similar to
that of alfalfa (Medicago sativa L.). Kenaf can be ensilaged
effectively, and as such has satisfactory digestibility, and an outstanding
amount of digestible protein (Wing 1967). Digestibility of dry matter and
crude proteins for kenaf feeds have ranged from 53.5 to 82.4%, and 59 to 70.6%
respectively (Phillips et al. 1989; Powell and Wing 1967; Suriyajantratong et
al. 1973; Swingle et al. 1978; Wing 1967). Kenaf meal, used as a supplement in
a rice ration for sheep, compared favorably with a ration containing alfalfa
meal (Suriyajantratong et al. 1973). Clark and Wolff (1969) determined that
crude protein content of kenaf decreased from 90 to 244 DAP. Powell and Wing
(1967) and Hurse and Bledsoe (1989) have reported whole plant kenaf yields of
13.4 and 13.9 t/ha respectively at approximately 98 DAP. The objective of the
forage evaluation research was to determine the effect of cultivars and harvest
date on plant growth, protein content, and kenaf dry matter yields.

In 1989, and 1990, a research study was conducted at Ladonia, Texas (Lat.
33°, Long. 96°) which included six kenaf cultivars and three harvest
dates. The six kenaf cultivars evaluated were 'Guatemala 4', 'Guatemala 45',
'Guatemala 48', 'Guatemala 51', 'Cuba 2032', and 'Everglades 41'. Each
cultivar was harvested at 76, and 99 DAP to evaluate kenaf as a livestock feed.
A full season harvest sample was also collected at 184 DAP (27 Oct. 1989) and
154 DAP (25 Oct. 1990) to comparatively evaluate the cultivars as a source of
fiber. The experiments were planted on 26 Apr. 1989 and 24 May 1990. Plots
were 3 by 6 m with 50 cm row spacing. A 2.25 m2 (1.5 by 1.5 m)
quadrant was harvested from the center three rows of each plot. The plants in
the entire quadrant were harvested at ground level and weighed to determine the
fresh weight of plants per hectare. Three plants from this area were measured
for plant height, and vegetative growth stage (V-Stage). The kenaf vegetative
growth stage was determined by adapting the soybean [Glycine max (L.)
Merrill] index system developed by Fehr et al. (1971) to kenaf. The index
system counts the number on vegetative nodules on the primary plant stalk.
Leaves and reproductive parts (flowers and flower buds) were removed and stalks
cut into 20 cm lengths. Leaves, reproductive parts, and stalks were weighed
before and after being oven dried at 66°C for 48 h. Total dry matter, stalk
yields, percent leaves, and percent stalks were based on oven dry weights.
Leaf, and stalk samples from harvest dates 76, and 99 DAP were ground using a
Wiley mill with a #10 mesh screen and then reground using a #20 mesh screen.
The Texas A&M analytical laboratory at College Station, Texas analyzed the
ground kenaf leaf and stalk samples for crude protein (Techcon Method
334-74-W/B).

The studies were randomized complete block designs with four replications and
mean differences were determined using a least significant difference (LSD)
test level of 0.05 as described by Snedecor and Cochran (1967).

'Guatemala 4' was shorter than all other cultivars except 'Everglades 41'
(Table 1). Vegetative development was greater for 'Guatemala 45' than either
'Guatemala 4' and 'Cuba 2032' (Table 1). Cultivars and harvest dates affected
the percentage of kenaf leaves (Table 1). 'Guatemala 45' with 31% leaves was
significantly greater than either Guatemala 48 or Everglades 41 (Table 1).
Other researchers have also reported significantly less leaf percentages for
'Everglades 41' compare to other cultivars (Wilson et al. 1965; Webber 1990b).
Percent leaves decreased 36% for the first harvest to 20% for the third harvest
(Table 1). As kenaf plants increase in height and maturity, the lower leaves
senesce, resulting in a decreased percentage of leaves (Webber 1990b; Clark and
Wolff 1969).

'Guatemala 48', 'Everglades 41', and 'Cuba 2032' had significantly greater
whole plant yields than either 'Guatemala 4' or 'Guatemala 45' (Table 2). The
combination of high whole plant protein and whole plant yields for Guatemala 48
resulted in this cultivar yielding the greatest total crude protein produced
per ha (Table 2).

The selection of a harvest date and kenaf cultivar are important variables in
producing maximum protein and dry matter yields. 'Guatemala 48' percent whole
plant protein was greater than 'Cuba 2032' and greater than all other cultivars
in its production of crude protein production per ha (Table 2). An early
harvest date (76 DAP) produced the greatest percentage leaf, stalk, and whole
plant protein (Table 2). Kenaf can produce a large amount of dry matter, 7,512
kg/ha, within 90 DAP (Table 1). Results suggest that kenaf should continue to
be studied, not only as a fiber crop for the production of paper pulp, but as a
viable source for livestock feed. Future research should focus on differences
in percent crude protein between cultivars, and maximizing total protein
production per ha.

The possible acceptance of kenaf as a commercial crop within the United States
is increased as additional production, harvesting, processing, and product
development evaluations are conducted. The establishment of small diversified
uses for kenaf may offer certain advantages over the large capital investment
in a single large kenaf paper or newsprint mill. The increased production,
processing, and product development work being conducted within private
industry is encouraging and suggests a bright future for the establishment of
kenaf as a commercial crop within the United States.

*We acknowledge David A. Iverson, Research Technician, Agricultural Research
Service, South Central Agricultural Research Laboratory, Lane, Oklahoma for
field plot work, data entry, and data analysis; Vee Hiltbrunner-Bledsoe, Leon
Hurse, and Foy Burns for their constant encouragement and support.
Table 1. Two year means of yield components of kenaf as influenced by
cultivars and harvest dates.

Variable

Height(cm)

V-Stage(no.)

Leaves(%)

Total dry matter(kg/ha)

Cultivarz

Everglades 41

180

54.4

27

9160

Cuba 2032

185

50.8

28

9195

Guatemala 4

171

50.7

29

7883

Guatemala 45

183

56.1

31

7713

Guatemala 48

187

54.9

28

9345

Guatemala 51

185

52.8

30

8831

LSDy (0.05)

10

4

3

1269

Harvest datex

76 DAP

123

32.7

36

4764

99 DAP

171

48.7

30

7512

169 DAP

252

78.4

20

13788

LSDw (0.05)

7

3

2

898

zCultivar means averaged over three harvest dates.yLSD for comparison between cultivars.xHarvest means averaged over six cultivars.wLSD for comparison between harvest dates.
Table 2. Two year means of crude protein percentages and whole plant
protein yields as influenced by cultivars and harvest dates.

Crude protein

Variable

Leaves(%)

Stalks(%)

Whole plant(%)

Whole plant(kg/ha)

Cultivarz

Everglades 41

15.2

3.0

6.9

436

Cuba 2032

14.5

2.6

6.2

435

Guatemala 4

14.4

2.6

6.6

325

Guatemala 45

14.9

2.9

7.2

369

Guatemala 48

15.5

2.8

7.2

558

Guatemala 51

14.9

2.8

6.7

395

LSDy (0.05)

NS

NS

0.9

116

Harvest datex

76 DAP

15.6

3.2

7.7

390

99 DAP

14.2

2.4

5.9

449

LSDw (0.05)

0.7

0.3

0.5

NS

zCultivar means averaged over two harvest dates (76 and 99 DAP).yLSD for comparison between cultivars. xHarvest means averaged over six cultivars. wLSD for comparison between harvest dates.
Last update April 23, 1997
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